1. Field of the Invention
The present invention relates to a communication system and data transmission method thereof. More particularly, the present invention relates to a communication system and data transmission method thereof that efficiently transmits data to user equipment when a handover is performed between evolved Node Bs (eNBs).
2. Description of the Related Art
In general, Universal Mobile Telecommunication Systems (UMTS) refer to a third (3rd) generation communication system that is based on a Global System for Mobile communications (GSM) and General Packet Radio Services (GPRS), and uses Wideband Code Division Multiple Access (WCDMA). A 3rd Generation Partnership Project (3GPP) for standardizing the UMTS has proposed an Evolved Packet System (EPS), such as a Long Term Evolution (LTE) system, where the EPS is a next generation communication system of the UMTS. The LTE system refers to a technology for implementing fast packet based communication.
In the next generation communication system, while a source eNB downloads source data, a handover of user equipment may be performed from the source eNB to a target eNB. In that case, the source eNB forwards the source data to the target eNB. The target eNB downloads the source data and target data following the source data.
However, the target eNB has difficulty in determining the transmission order between the source data and the target data. That is, the target eNB cannot precisely identify a time point to transmit target data to user equipment.
Therefore, a need exists for a communication system and data transmission method for determining a transmission order between source data and target data, and for identifying a time point to transmit the target data.